JP2821807B2 - Ultrasonic motor drive controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application of the Present Invention> The present invention relates to a drive control device for an ultrasonic motor.

<Related Art and Problems to be Solved> In recent years, since there is no generation of magnetism, the size is small, and the torque is large, an ultrasonic motor is used as a drive source of various devices.

Ultrasonic motor, as shown in FIG. 8, a disk-shaped rotor 2 having a rotating shaft 1 to the center, arranged in a ring plurality of piezoelectric _{3 1 ~3 n, 4 1 ~4} n, 5 and a stator 8 having an elastic body 7 adhered to the upper surface of the piezoelectric sensor 6.

The piezoelectric element 3 ₁ to 3 _n, 4 ₁ to 4 _n are aligned so polarities are alternately arranged, as shown in FIG. 9, left piezoelectric member 3 ₁ -
3 _n and against the right side of the piezoelectric element 4 ₁ ~4 _n, 90 ° phase at a frequency close to the resonant frequency of the piezoelectric body is different alternating signal electrodes 9a, 9
b, 10a, is applied from 10b, the piezoelectric 3 ₁ ~3 _n, 4 ₁ ~4
_n vibrates flexurally in the circumferential direction, and the left and right waves interfere with each other via the intermediate piezoelectric body 5, and as shown in FIG. 10, the surface of the elastic body 7 travels along the circumferential direction. Elastic waves are generated.

For this reason, the rotor 2 in contact with the elastic body 7 from above
Is driven to rotate in the direction opposite to the direction in which the elastic wave travels.

The rotation speed of the rotor 2 is such that as the amplitude of the elastic wave increases, the delay with respect to the traveling speed of the elastic wave decreases, and the amplitude of the elastic wave decreases as shown by the characteristic A in FIG. closer to the piezoelectric element _{3 1 ~3 n, 4 1 ~4} n resonant frequency F ₀ of the increase.

Therefore, if the AC signal frequency for the ultrasonic motor is varied in the range of, for example, Fa to Fb, the motor rotation speed also changes following the variation of this frequency.

However, this ultrasonic motor, even when the power supply is not performed, since the rotor 2 in the elastic body 7 of the stator 8 is pressed, by applying a sudden alternating signal close to the resonance frequency F ₀ at start In many cases, startup does not occur smoothly.

For this reason, in the drive control device of the ultrasonic motor, at startup, the frequency of the AC signal is swept from the frequency Fc higher than the frequency at the time of steady rotation to the Fb side at a predetermined speed, and gradually changes from low-speed rotation to high-speed rotation. I try to make it start smoothly.

However, the resonance characteristics of the ultrasonic motor greatly change depending on the ambient temperature, and especially at low temperatures, the characteristic A at normal temperature in FIG. 11 shows the characteristic B having a sharper curve at a resonance frequency F ₀ ′ higher than F ₀ . It shifts like this.

If an ultrasonic motor with low mechanical startability at low temperature is started at the same sweep speed as at room temperature at such low temperature, the operation of the motor cannot catch up, and the frequency of the AC signal becomes the resonance frequency. And could not be started.

An object of the present invention is to provide a drive control device for an ultrasonic motor that solves this problem.

<Means for Solving the Problems> In order to solve the above problems, a drive control apparatus for an ultrasonic motor according to the present invention includes a drive control device for an ultrasonic motor, which detects a frequency sweep speed of an AC signal at startup by a temperature sensor. Variable control is performed according to the level of the ambient temperature.

<Operation> Therefore, the frequency sweep of the AC signal at the time of low temperature startup is performed at a lower speed than the frequency sweep at the time of high temperature startup.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing a configuration of a drive control device (hereinafter referred to as a drive control device) 20 for an ultrasonic motor according to one embodiment.

In FIG. 2, reference numeral 21 denotes a DA converter that outputs a voltage corresponding to output data from the CPU 30 described later, and 24 oscillates a signal whose frequency changes in a direction opposite to a change in the output voltage of the DA converter 21. It is a VCO (voltage controlled oscillator) to output.

Reference numeral 23 denotes a phase shift circuit that generates an AC signal having a phase difference of 90 degrees by dividing the output signal from the VCO 22 by 1/4.

24 and 25 is a driver for applying each amplify the output of the phase shift circuit 23 to the piezoelectric member _{3 1 ~3 n, 4 1 ~4} n of the ultrasonic motor M.

A rotary encoder 26 that outputs a pulse signal having a frequency proportional to the rotation speed of the rotor 2 is connected to the rotor 2 of the ultrasonic motor M.

27 is a temperature sensor that outputs a signal corresponding to the ambient temperature of the ultrasonic motor M, and 28 is the 2-bit temperature data shown in FIG. 3 according to the range of the detected temperature, receiving the output of the temperature sensor 27. Is an AD converter that outputs.

Reference numeral 29 denotes a speed setting device for setting a steady speed (target speed) of the ultrasonic motor M, and sets a pulse period T of the rotary encoder 26 when the ultrasonic motor M rotates at the target speed.

As shown in FIG. 4, the CPU 30 calculates the coefficient values A _{1 to} A ₄ (where 0 <A ₁ <A ₂₎ corresponding to the temperature data from the AD converter 28.
<A ₃ <A ₄ ) is stored in the memory 31 and the activation signal is “H”
When the level is reached, the VCO 22 is swept to start the ultrasonic motor M based on the coefficient value for the temperature data at that time.

FIG. 1 is a flowchart showing the startup processing of the CPU 30, and the operation of the drive control device 20 will be described below according to this flowchart.

When the activation signal goes "H" level for CPU 30, the coefficient for the temperature data from the AD converter 28 is determined to be any one of A ₁ to A ₄ (Step 1).

Next, voltage data D for the DA converter 21 is set to an initial value D ₀ (Step 3).

Therefore, the frequency corresponding to the voltage data D ₀ (e.g. the
The two-phase AC signal of Fc) in FIG. 11 is applied to the ultrasonic motor M.

The application of the AC signal causes the ultrasonic motor M to gradually rotate, and a pulse signal having a long cycle is output from the rotary encoder 26, and the cycle t is measured (step 4).

Next, the voltage data D is increased by a value obtained by multiplying the value obtained by subtracting the period T set in the speed setting unit 29 in advance from the measured period t by the coefficient A, and new voltage data D + A Driving is performed by an AC signal having a frequency corresponding to (t-T) (step 5).

Next, the two periods t and T are compared in magnitude. If the period t of the output pulse of the rotary encoder 26 is longer than the set period T, the process returns to step 4 (step 6).
Hereinafter, the same processing (step 4) until the cycle t of the output pulse of the rotary encoder 26 becomes shorter than the set cycle, that is, until the rotation speed of the ultrasonic motor M reaches the target speed.
6) are performed.

At this time, the change width of the voltage data every time, that is, the change width of the frequency of the AC signal is smaller as the coefficient A corresponding to the ambient temperature is smaller, so that the frequency sweeping speed when started at a low temperature is higher than that at a high temperature. As a result, the motor operation is reliably started without delaying this driving.

In this way, when the ultrasonic motor M is started up to the target speed, the CPU 30 shifts to a constant speed control process.

FIG. 5 is a flowchart showing the constant speed control process. After the start-up process, the level of the start-up signal is determined.
Is measured, and the magnitude of the measured cycle t is compared with the set cycle (steps 7 to 9).

Here, if t = T, it is determined that the rotation speed is equal to the target speed, and the process returns to step 8. If t <T, it is determined that the rotation speed is higher than the target speed, and the voltage data is A ·. The value is subtracted and updated by P (P is a constant), and the frequency of the AC signal is increased (step 10).

If t> T, it is determined that the rotation speed is lower than the target speed, the voltage data is added and updated by A and P, and the frequency of the AC signal decreases (step 11).

Therefore, the rotation speed of the ultrasonic motor M after starting is
The constant speed control is always performed at the target speed.

<Another embodiment of the present invention> In the above embodiment, the cycle of the output pulse of the rotary encoder 26 is measured and the speed control is performed by the CPU 30. However, a drive control device having an analog control unit is described. The present invention can also be applied.

FIG. 6 is a circuit diagram showing a case where the present invention is applied to an analog control circuit 35.

In the control circuit 35, a pulse of a predetermined width synchronized with the output pulse of the rotary encoder 26 is output from the one-shot multi-circuit 36, and the output is integrated by an integration circuit 37, thereby performing frequency-voltage conversion. Va
And the reference voltage Vr from the variable resistor 38 as an analog adder
It is configured to control the oscillation frequency of the VCO 22 with the voltage V ₀ added in 39, and when the rotation speed of the ultrasonic motor M is higher than the target speed (corresponding to the reference voltage Vr),
If the oscillation frequency of the VCO 22 is increased, and conversely, if it is slow, the oscillation frequency of the VCO 22 is decreased to always approach the target speed.

Capacitor provided between input and output of analog adder 39
C ₁ , C ₂ , and C ₃ are capacitors for determining the response speed of the output with respect to the input voltage V ₀ of the VCO 22, and correspond to the coefficients A _{1 to} A ₄ in the embodiment (where C ₁ <C ₂ <C _3).

The connection of the capacitors C ₂ and C ₃ is made by switches 40 and 41 which are turned on when the temperature data from the AD converter 28 is “0”,
As shown in FIG. 7, the connection is made such that the parallel capacitance increases as the temperature decreases.

Therefore, for example, when the motor is started (when power is turned on) at a low temperature of −20 degrees, only the reference voltage Vr is applied to the analog adder 39, and the output is slow due to the capacitance of C ₁ + C ₂ + C _3. Since the response speed changes slowly, the frequency sweeping speed of the AC signal applied to the ultrasonic motor M is also low, and the motor is reliably started.

With this start, the motor rotation speed approaches the target speed, the loop becomes substantially equilibrium, and a constant speed control state is set.

Even in this state, the output change of the analog adder 39 with respect to the change of the output voltage Va of the integration circuit 37 is slower as the temperature is lower, so that the rate of change of the rotation speed is almost uniform over the entire temperature range.

<Effects of the Present Invention> As described above, the drive control apparatus for an ultrasonic motor according to the present invention controls the speed of frequency sweeping at the time of starting an AC signal applied to the ultrasonic motor by detecting the speed around the motor detected by the temperature sensor. Since it can be changed according to the level of the temperature, the motor can always be started reliably regardless of the ambient temperature.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a startup control according to an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of the embodiment, and FIGS. FIG. 5 is a flow chart showing the processing procedure of the constant speed control of one embodiment. FIG. 6 is a circuit diagram showing a control unit according to another embodiment of the present invention,
FIG. 7 is a correspondence diagram for explaining the operation of the main part of the embodiment of FIG. FIG. 8 is a schematic perspective view showing the configuration of an ultrasonic motor, and FIG.
The figure is a front view of a main part of the ultrasonic motor, and FIG. 10 is a schematic view for explaining the operation of the ultrasonic motor. FIG. 11 is a diagram showing characteristics of an elastic wave amplitude with respect to a driving frequency of an ultrasonic motor. 20 …… Ultrasonic motor drive controller, 22 …… VCO, 23…
... Phase shift circuit, 26 ... Rotary encoder, 27 ... Temperature sensor, 29 ... Speed setting device, 30 ... CPU, M ... Ultrasonic motor.

Claims (1)

(57) [Claims] 1. A drive of an ultrasonic motor for starting an ultrasonic motor by sweeping a frequency of an AC signal applied to the ultrasonic motor in a resonance frequency direction of a piezoelectric body constituting a stator of the ultrasonic motor. A control device for an ultrasonic motor, wherein the control device variably controls a frequency sweep speed of the AC signal at the time of starting according to a level of an ambient temperature of the ultrasonic motor detected by a temperature sensor.